CVE-2026-90467 cole CVE debrief

Who should care

Defenders responsible for email infrastructure, developers using aiosmtplib, and security teams monitoring for suspicious email activity should assess exposure and prioritize remediation.

Why it matters

The aiosmtplib ESMTP parameter injection vulnerability allows attackers to manipulate email commands, potentially leading to identity forgery and delivery notification abuse. Defenders should verify email address validation, upgrade to version 5.1.3 or later, and monitor for suspicious email activity.

• Potential for forged authenticated identities
• Forced delivery notifications to third parties
• Possible abuse of email services

Technical summary

The aiosmtplib library before version 5.1.3 fails to properly validate email addresses, allowing attackers to inject ESMTP parameters into MAIL FROM and RCPT TO command lines. This can lead to forged authenticated identities or forced delivery notifications to third parties. The vulnerability is caused by inadequate validation of email addresses, which enables attackers to craft malicious addresses containing spaces and angle brackets to append parameters like AUTH, NOTIFY, or ORCPT to envelope commands. Defenders should prioritize verifying email address validation in aiosmtplib and upgrading to version 5.1.3 or later.

Defensive priority

Defenders should prioritize verifying email address validation in aiosmtplib and upgrading to version 5.1.3 or later.

Recommended defensive actions

• Verify email address validation in aiosmtplib
• Upgrade to aiosmtplib version 5.1.3 or later
• Monitor for suspicious email activity
• Review compensating controls for exposed systems
• Check relevant monitoring, detection, and logs for exposed assets
• Track exceptions and retest remediated assets
• Plan vendor-supported updates or mitigations

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but the scope of affected deployments and specific exploitation attempts are not documented in the provided sources. The aiosmtplib library is widely used in email infrastructure, and defenders should verify email address validation and monitor for suspicious email activity. The vulnerability has a CVSS score of 6.3 and is considered medium severity.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.